As is familiar with magnetic card readers, a card usually is placed into a slot and is then moved with respect to a delicate head assembly. Typically, such a reader contains a variety of elements which are required to cooperate in a way which is precisely prescribed in order to be able to read (or write) magnetic indications on the card. Drive belts may be employed to ensure the desired cooperation. But drive belts are costly. Alternatively, gear trains may be used. However, suitable gear trains require a high degree of precision. Moreover, the various forms of looseness (e.g. shaft endplay, gear backlash) and imperfection (e.g. shaft eccentricity, gear tooth irregularity) characteristic of gear tains often combine to introduce irregular extraneous motions which are transmitted by the rigid mechanical coupling to the driven member. This irregular motion, or jitter, causes errors in both reading and writing.